This study examines the relationships among severity of illness, quality of life, and functional ability and determines the impact of oxygen therapy on the functional ability of patients with alpha-I antitrypsin deficiency. Adult alpha-I antitrypsin deficient patients, admitted for evaluation of their lung disease, respond toga questionnaire that measures four aspects of their quality of life: emotional function, fatigue, mastery, and dyspnea. Patients walk for 6 minutes with oxygen via nasal cannula or with placebo. Measurements include distance walked, oxygenation and pulse rate during the walk, and dyspnea intensity at the end of each walk. To date, we have collected data on 33 subjects. Data analysis indicates no advantage of oxygen over placebo in terms of the outcome measures. Accrual of subjects for this portion of the study has stopped. An amendment to this protocol was approved for test patients in more advanced stages of the disease, comparing oxygen with paced breathing. Twenty subjects have been accrued thus far for this amendment. Data collection and subject accrual will continue.